In manufacturing integrated circuits and active elements and interconnecting structures within microelectronic devices, a photolithography technique using photoresist compositions is utilized. In general the manufacturing of the integrated circuits or microelectronic devices are conducted as followed. That is, first, a photoresist material dissolved in a solvent is applied on a substrate such as silicon wafer by spin coating. The substrate coated with resist is then baked at elevated temperatures to evaporate any solvent in the photoresist composition and to form a thin photoresist layer with good adhesion to the substrate. The thin photoresist layer on the wafer was subjected to an imagewise exposure to radiation in the range of 150 to 450 nm wavelength, such as visible or ultraviolet (UV) rays. The imagewise exposure may also be conducted by electron beam or X-ray radiation in place of such visible or UV rays. In the exposed areas of the photoresist layer the chemical transformation arises by the exposure. After the imagewise exposure, the substrate with an imagewise exposed resist layer was subjected to developing process using an alkaline developer to dissolved out either the unexposed (negative-working resist) or exposed (positive-working resist) areas. The opened areas on the substrate formed by dissolving out the resist are subjected to additional unselective processing steps to manufacture final integrated circuits or electronic devices.
In manufacturing integrated circuits and the like, the high degree of integration has been intended and, in recent years, in order to attain a higher degree of integration techniques for still more decreasing feature sizes are required. Therefore lithographic techniques using conventional near UV, such as g-line (436 nm) and i-line (365 nm) shift to imaging processes using radiation of shorter wavelength, such as middle UV (350-280 nm), or deep UV (280-150 nm). The latter especially employs KrF (248 nm) or ArF (1 93 nm) excimer laser radiation. Excimer laser radiation sources emit monochromatic radiation. Highly sensitive, excimer laser compatible chemically amplified, positive- or negative-working deep UV photoresist compositions offering excellent lithographic performance and high resolution capability have become available recently. Due to their chemical compositions and their image formation mechanisms, state-of-the-art chemically amplified photoresist compositions are usually transparent at the exposure wavelength, and do not exhibit a pronounced sensitivity owing to poisoning effects induced by base contaminants present at the photoresist-substrate or photoresist-air interfaces, respectively. While appropriate deep-UV exposure tools in combination with the high performing photoresists are capable of patterning structural elements with dimensions below quarter micron design rules, tendency of arising image distortions and displacements due to some optical effects become conspicuous in such high resolution image. Therefor the method of forming resist images not affected by such optical effects and having good reproducibility are strongly required.
One of the problems caused by such optical effects is "standing wave" formation which is well known in the art and arise from substrate reflectivity and thin film interference effects of the monochromatic radiation. Another problem is "reflective notching" known in the art due to light reflection effects resulting from highly reflective topographic substrates. In single layer resist processes it is difficult to conduct the linewidth uniformity control due to the reflective notching. Certain reflective topographical features may scatter light through the photoresist film, leading to linewidth variations, or in other case, resist loss. Such problems are extensively documented in the literature, e.g. (i) M. Horn, Solid State Technol., 1991(11), p. 57 (1991), (ii) T. Brunner, Proc. SPIE 1466, p. 297 (1991), or (iii) M. Bolsen et al., Solid State Technol., 1986(2), p. 83, (1986).
Thin film interference generally results in changes of linewidth by variations of the substantial light intensity in the resist film as the thickness of the resist changes. These linewidth variations are proportional to the swing ratio (S) defined by following equation (1) and must be minimized for better linewidth control. EQU S=4(R.sub.1 R.sub.2).sup.1/2 e.sup.-.alpha.D (1)
Wherein R.sub.1 is the reflectivity at the resist-air interface, R.sub.2 is the reflectivity of the resist-substrate interface, .alpha. is the resist optical absorption coefficient, and D represents the resist film thickness.
One of lithographic techniques to overcome the above-mentioned problems during pattern formation on reflective topography is addition of radiation absorbing dyes to the photoresists as described in U.S. Pat. Nos. 4,575,480 or 4,882,260. This corresponds to an increase of the optical absorption coefficient a in equation (1) above. When a dye is added to the photoresist to form a radiation sensitive film having high optical density at the exposure wavelength, drawbacks such as loss of resist sensitivity, resolution and depth-of-focus capability, contrast deterioration, and profile degradation are encountered. In addition, difficulties during subsequent hardening processes, thinning of the resists in alkaline developers and sublimation of the dye during baking of the films may be observed.
Top surface imaging (TS1) processes, or multi layer resist arrangements (MLR) as described in U.S. Pat. No. 4,370,405 may help prevent the problems associated with reflectivity. However, such methods require complex processes and are not only difficult to control the processes but also expensive and therefore not preferred. Single layer resist (SLR) processes dominate semiconductor manufacturing because of their simplicity and cost-effectiveness.
The use of either top or bottom anti-reflective coatings in photolithography is a much simpler and effective approach to diminish the problems that arise from thin film interference, corresponding to either a decrease of R.sub.1 or R.sub.2 and thereby reducing the swing ratio S.
The most effective means to eliminate the thin film interference is to reduce the through the use of so-called bottom anti-reflective coatings (BARC). These coatings have the property of absorbing the light which passes through the photoresist and not reflecting it back. The bottom anti-reflective coating composition is applied as a thin film on the substrate prior to coating with the photoresist composition. The resist is then applied on the bottom anti-reflective coating, exposed and developed. The anti-reflective coating in the resist removed areas is then etched, for example in an oxygen plasma, and the resist pattern is thus transferred to the substrate allowing for further processing steps for forming active elements, interconnecting structures etc. The etch rate of the anti-reflective coating composition is of major importance and should be relatively higher than that of the photoresist, so that it is etched without significant loss of the photoresist film during the etch process.
Bottom anti-reflective coatings are typically divided into two types, namely inorganic and organic bottom anti-reflective coating types.
Inorganic types include stacks of dielectric anti-reflective coatings such as TiN, TiON, TiW and spin-on glasses useful in a thickness range of below 300 .ANG.. Examples are described by (i) C. Noelscher et al., Proc. SPIE 1086, p. 242 (1989), (ii) K. Bather et al., Thin Solid Films, 200, p. 93 (1991), or (iii) G. Czech et al., Microelectr. Engin., 21, p. 51 (1993). Although inorganic dielectric anti-reflective coatings effectively reduce thin film interference effects, they require complicated and precise control of the film thickness, film uniformity, special deposition equipment, complex adhesion promotion techniques prior to resist coating, separate dry etching pattern transfer step, and are usually difficult to remove.
Improved linewidth and standing wave control can also be attained by use of organic bottom anti-reflective coating as same as inorganic type. As organic bottom anti-reflective coatings it is known ones formulated by adding dyes which absorb at the exposure wavelength to a polymer film, as described by C. H. Ting et al., Proc. SPIE 469, p. 24 (1984), or W. Ishii et al., Proc. SPIE 631, p. 295 (1985). Problems of the anti-reflective coatings produced as described above include (1) separation of dye and polymer during spin coating, drying, or baking, (2) sublimation of the dye during the subsequent hard-bake step, (3) dye stripping into resist solvents, (4) thermal diffusion into the resist upon the baking process and (5) interfacial layer formation. These phenomena may cause severe degradation of lithographic properties especially when combined with chemically amplified photoresists and therefore the method of using dye blended bottom anti-reflective coatings are not preferred. Especially problematic is the sublimation issue, as not only the absorption properties of the bottom anti-reflective coating are deteriorated, but also contamination of the expensive equipment must be anticipated, causing process problems due to increased particle concentrations at a later stage.
As an alternative, organic bottom anti-reflective coatings containing radiation absorbing pigments have been suggested (EP-A1 744662). Such bottom anti-reflective coatings may produce a large number of insoluble particles during device processing and thereby reduce yield considerably.
Direct chemical attachment of dyes to a film forming polymer is another option (US patent 5,525247). The materials disclosed therein are usually casted from hazardous organic solvents, such as cyclohexanone or cyclopentanone. M. Fahey et al., Proc. SPIE 2195, p. 422 (1994) describe amino group-containing dyes reacted with the anhydride groups of poly(vinylmethylether-co-maleic anhydride). One problem connected with these types of bottom anti-reflective coating compositions is that the reaction between the amine and the polymeric anhydride groups does not proceed quantitatively thus resulting in the presence of free amines (EP-A1 583,205, p. 5, lines 17-20). The unreacted amine causes poisoning of the resist at the bottom anti-reflective coating-resist interface especially when base sensitive chemically amplified resist compositions are employed resulting in resist foot formation due to incomplete dissolution of the exposed resist bottom layer upon development. The free dye molecules may also sublime during the baking process, deposit on the fabrication instruments and cause contamination problems as well as health hazard to the workers. One more disadvantage of these specific composition is that imide compounds formed upon the reaction between the amine and the anhydride groups are poor in their solubility and require polar solvents for their processing not used normally in photoresist formulations. From the processing standpoint, it would be ideal to use the same solvent for photoresist and for bottom anti-reflective coating. Furthermore, water which is formed as the by-product of the imidization reaction may cause coating defects (pinholes) during film formation.
Another system which Fahey et al. propose in the above mentioned publication is based on materials composed from copolymers of methyl methacrylate and 9-methylanthracene methacrylate. However, formulations based on these copolymers usually show footing due to the diffusion of photo generated acid into the bottom anti-reflective coating film as well as intermixing of the resist and the bottom anti-reflective coating film thus limiting their practical use. The copolymers are also insoluble in preferred photoresist solvents such as propylene glycol monomethyl ether acetate (PGMEA) or ethyl lactate (EL).
U.S. Pat. Nos. 5,234,990 and 5,578,676 describe polysulfone and polyurea resins which possess inherent light absorbing properties at deep ultraviolet wavelengths. However, these condensation products have comparatively poor film forming properties and therefore exhibit poor step-coverage on topographic substrates, resulting in a problem of image transfer to the substrate. In addition, it has been found that these materials exhibit a high degree of crystallinity and tend to form cracks probably due to their high Tg and rigid structures. Initially, a bottom anti-reflective coating should be soft to achieve good step coverage properties upon coating and in addition should have the ability to crosslink and harden after baking to prevent intermixing of the photoresist with the bottom anti-reflective coating layer as well as diffusion of the photo generated acid.
U.S. Pat. No. 5,554,485 and EP-A1 698823 describe poly(arylether) or poly(arylketone) polymers respectively. These polymers have a rather high concentration of aromatic units and therefore their etch rates are rather low. That is same for the polyvinylnaphthalene derivatives disclosed in U.S. Pat. No. 5,482,817.
EP-A1 542008 describes the use of phenolic type resin binders and melamine type crosslinking agents in combination with either thermal, or photo acid generators to harden the bottom anti-reflective coating film after coating. Such compositions are poor in their storage stability due to the presence of the crosslinking agents and photo acid generators resulting in high film defect yields. In addition, their etch rate is very low due to the presence of rather large amounts of aromatic functional groups.
Japanese Laid-opened Patent Publication No. H10-221855 discloses an anti-reflective coating material composition containing a high molecular compound in which choromophores having 10,000 or more of molar extinction coefficient for either 365 nm, 248 nm or 193 nm wavelength radiation are linked to at least a part of alcohol moieties of recurrent vinyl alcohol units in main chain and a method of producing resist patterns. However introduction of such bulky polycyclic aromatic group alone into a high molecular compound containing recurrent vinyl alcohol such as polyvinyl alcohol by acetalization reaction requires elevated temperature and long time reaction. In addition it is difficult to attain high reaction percentage. The publication disclose that expected yield is attained when the reaction was conducted in dioxane at 100.degree. C. for 40 hours. However the organic chromophore groups are easy to decompose under such reaction conditions and it is necessary to moderate the reaction conditions.
In summary, a superior bottom anti-reflective coating material should satisfy the following requirements:
a) good film forming property PA1 b) high absorption at the applied exposure wavelength PA1 c) no intermixing with the photoresist PA1 d) high etch rate compared with the photoresist PA1 e) good step coverage on topography PA1 f) practical storage stability PA1 g) compatibility with and solubility in photoresist and edge-bead rinse (EBR) solvents PA1 h) adaptability to several commercial resists PA1 i) ease of production and high yield.
The object of the present invention is to provide an anti-reflective coating composition satisfying above preferable properties, a method of manufacturing integrated circuits using the composition, novel polymer dyes and a method of preparing thereof.
Definitely, the first objective of the present invention is to provide a bottom anti-reflective coating composition which absorbs radiation in the wavelength range of 150-450 nm thus eliminating problems associated with light reflected from the substrate and topography during pattern formation.
The second objective of the present invention is to provide a bottom anti-reflective coating composition having improved adhesion to integrated circuit or micro-electronic substrates, very good coating uniformity and showing no particle formation.
The third objective of the present invention is to provide a bottom anti-reflective coating composition with a superior etch rate than current available bottom anti-reflective coatings, having improved compatibility with the existing chemically amplified photoresists, and generating neither undercut nor footing.
The fourth objective of the present invention is to provide novel polymeric dyes having cyclic acetal moieties and applicable for a bottom anti-reflective coating composition as well as producible easily and in high yield and a method of preparing thereof.
The fifth objective of the present invention is to provide bottom anti-reflective coating compositions comprising of polymeric dyes having cyclic acetal moieties, together with, if necessary, crosslinking agents and other additives such as photo acid generators, plasticizers or surfactants.
The sixth objective of the present invention is to provide novel polymer and copolymer materials producible easily and in high yield, and capable of curing (crosslinking) at the baking temperatures of the resulting bottom anti-reflective coating to harden the bottom anti-reflective coating thus providing a barrier for photoresist solvent or component penetration and thereby preventing foot formation caused by either intermixing or acid diffusion.
The invention further provides a method for application and use of the anti-reflective coating composition in combination with a photoresist on a substrate useful in manufacturing integrated circuits and micro-electronic devices. Thus in a preferred aspect, a method is provided, comprising the steps of; 1) treating a substrate with a primer, 2) applying the bottom anti-reflective composition of the present invention, 3) baking the coated bottom anti-reflective coating film to evaporate the solvent and to harden the film, 4) applying a photoresist on top of the bottom anti-reflective coating, 5) drying the photoresist, 6) exposing the photoresist using a mask, 7) developing the resist and 8) removing the bottom anti-reflective coating in the opened areas.
Other objects will become apparent from the following detailed description, preferred embodiments and illustrative examples mentioned below.